Diamond is the allotrope of carbon which, when pure, provides it the following properties:
Hardness: 10 on the mohs scale (10=hardest); electrical resistance: 1018 Ω·m; thermal conductivity: ˜2500 W·m/m2 (Cu=385 W·m/m2); refractive index: 2.417; dielectric constant/strength: 5.6, 107V/cm; band gap: 5.45 eV; mobility: 1,600 cm2/Ns; oxidation temperatures: air:=˜1000° C., O2=˜600° C.; graphite transformation temperature (vacuum, inert atmosphere): ˜1,500° C.; widest known transmission spectrum: 220 nm to >50 μm—x-ray, infrared, terahertz and microwave; highly chemical inert; lowest coefficient of thermal expansion: 1.1-1.3 (Invar=1.4); solid surface friction (surface passivated): <0.1.
In addition to its highly desirable physical properties, diamond is a beautifully lustrous transparent crystal making it the “King” of gemstones.
A few of the numerous industrial applications which could exploit the highly desirable physical properties of very pure diamond include electronics and semi, conductors, optics and directed energy windows, mining and petrology, and bearings. Diamond is also used in detectors in particle physics experiments such as those in C.E.R.N. where fusion products cause doped diamond detectors to fluoresce. However, artificially produced diamond has not attained the level of purity in quantities which are economical and sufficient for extensive industrial use.
When pure, diamond is the ideal material for semi-conductor heat spreaders. Diamond, itself, may find use as a semi-conductor device material with its wide band gap. Boron doped diamond (blue diamond) is a p-type semiconductor. Quantum computing devices using nitrogen doped diamond are becoming commercially available. Diamond semi-conductors may have switching speeds of 80 Ghz or higher.
Diamond powder is pressed into and bonded with end effectors of mining and rock drilling bits at pressures around 1 million psi. Such bits typically comprise tungsten carbide containing a small percentage of cobalt powder, under high pressure, cobalt grows into the diamond (brachiation) to bond and adhere the diamond to the tungsten carbide. However, non-diamond carbon impurities in the diamond interfere with brachiation causing diamond to wear off before it wears out in use. Rock bits typically fail after 250 feet.
Turbine shaft bearings comprise metal shaft and race surfaces coated with tungsten carbide upon which diamond films are deposited. Between the shaft and race, surface passivated diamond powder is deployed to provide a low-friction, high temperature stable solid lubricant. Adhesion of the diamond layers to the tungsten carbide layers fails due to non-diamond impurities within the diamond layer leading to bearing failure.
The diamond products used in these limited examples of the industrial use of diamond are most often produced by either of the two most common diamond fabrication methods: HPHT (high pressure/high temperature) and CVD (chemical vapor deposition).
HPHT emulates the natural process of diamond formation deep within the earth's crust wherein elemental carbon is subjected to high temperatures, ˜2000° C., and high pressures, ˜1.5 million psi. Under these conditions, molten carbon forms diamond by assembly of carbon atoms about small diamond particles or diamond seeds. Product cycles range from about 3 weeks to 2 months. The apparatus required for HPHT diamond fabrication such as belt or cubic press type anvils is expensive and cumbersome. Small laboratory apparatus can cost several hundreds of thousand dollars.
CVD diamond fabrication processes grow diamond by energetic decomposition of a carbon source gas such as methane in a sealed chamber having a diamond forming surface heated to ˜800° C. bearing diamond particulates which function as the seed about which carbon atoms assemble to form diamond. Product cycles range from 2 weeks to 2 months. CVD processes produce more diamond per cycle than do HPHT processes, but there are higher labor, power, and support costs for CVD processes than for HPHT processes.
A need exists for methods of diamond fabrication which can provide high purity diamond products reliably, economically, and readily. Conventional diamond fabrication methods include HPHT (anvil or high pressure, high temperature) and CVD chemical vapor deposition. Thus far, these processes have not produced diamond products of requisite purity, but these processes do produce substantial quantities of diamond products which are used industrially.